AbstractSulphonic acids and carboxylic acids which do not react with thionyl chloride under normal conditions give the corresponding acid chlorides with this reagent in excellent yields when dimethylformamide is present as a catalyst.The reaction of thionylchloride with dimethylformamide yields the corresponding amide chloride which has not been isolated before in pure state. This amide chloride reacts with acids under formation of acid chlorides. The mechanism of these reactions is discussed.